Servicio de Información Comunitario sobre Investigación y Desarrollo - CORDIS

Component fluxes of net ecosystem CO2 exchange of mountain grassland ecosystems

The net ecosystem exchange of CO2 consists of several component processes, eg. above- and below-ground, auto- and heterotrophic. Understanding net ecosystem CO2 exchange under current climatic conditions and land use, and predicting net ecosystem exchange under likely future climatic conditions and land-use requires a quantification of the contribution of the various component processes and their interactions. This result delivers the required information on the component processes of the net ecosystem CO2 exchange of differently managed mountain grassland ecosystems in Europe. In the case of managed ecosystems CARBOMONT also quantifies off-site carbon losses, which need to be taken into account for an assessment of the carbon balance of managed (mowed or grazed) mountain grassland ecosystems.

- Leaf photosynthesis and respiration change with species/ functional group, nitrogen concentration, phenology and plant age. Thus, shifts in nitrogen supply, species composition and plant age structure as related to land-use changes immediately affect the physiological basis for gross primary production. A general relationship between the two main biochemical parameters used for modelling photosynthesis was confirmed.

- Variation among sites at different latitudes and elevations in the plant state spectrum was found to be the primary determinant of the apparent climatic sensitivity of functional leaf structure versus photosynthesis relations.

- Soil respiration is a major determinant of the carbon balance of grasslands, contributing the largest proportion to CO2 efflux from the ecosystems. Water-limited and water-logged sites exhibit distinct reductions of soil CO2 efflux. Management (mowing, grazing) may lead to a transient decrease of soil respiration.

- The proportion of root versus microbial contribution to soil respiration vary with site and type of land use and in response to management practices (e.g. cutting). Root diameter and nitrogen concentration affect the temperature sensitivity of root respiration and thus alter soil CO2 flux partitioning.

- The carbon cycle and its components are intimately linked to the nitrogen cycle, which depends on atmospheric deposition of nitrogen at a regional and fertiliser application at a local scale, both exhibiting peak values at the Central European sites. On intensively managed grasslands high N inputs result in the highest productivity, whose effect on net biome production is, however, counterbalanced by higher off-site C losses.

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University of Innsbruck, Institute of Botany
Sternwartestr. 15
6020 Innsbruck
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